The invention pertains to apparatus for the heat treatment of workpieces, especially to a furnace operated with hydrogen as a cooling gas under positive pressure for the hardening of metal workpieces. A housing encloses the heating chamber accepting a batch of workpieces and is attached to a vacuum pump. The housing is provided with gas inlets and gas outlets opening into the heating chamber; with a motor-blower unit, the impeller of which circulates the cooling gas; and with a heating system.
DE 34 16 092 to which U.S. Pat. No. 4,709,904 corresponds discloses a vacuum furnace for the heat treatment of a batch of metal workpieces, in which the container is evacuated after the batch has been placed inside and is then flooded with shielding gas. The batch is then raised to the maximum allowable working temperature of the circulation system by a heating system and by circulation of the gas; then it is heated to the desired final temperature of the heat treatment in the stationary shielding gas or under vacuum essentially by the action of thermal radiation. The device is equipped for this purpose with a closeable steel container and an internal heating chamber to accept the batch and with a gas blower and a gas guidance system for producing a circulating flow through the heating chamber. The essentially circular-cylindrical steel container is supported on a stationary support structure; its longitudinal axis is perpendicular to the ground, and an upper section can be lifted up from its supported lower section. The batch itself rests on a support stand, which is itself supported on the housing cover of the lower part.
A disadvantage of the known device is the nonuniform way in which the batch is both heated and cooled, primarily because of the location of the heating elements, which are installed only in the area of the central part of the housing, and also because of the routing of the cooling gas stream, which flows around the batch only in one direction and only peripherally.